This invention relates to means for preventing kickback of boards when ripping them with a circular saw. This kickback usually occurs when the piece being cut is caught by the rapidly rotating saw blade, and is propelled backwards. Various devices have been previously developed to prevent this. U.S. Pat. No. 3,232,326 shows a series of finger-like leaves of varying lengths having a gripping surface on the bottom depending from the splitter of a table saw. Radial arm saws commonly use fingers depending from an adjustable rod (for size of work) which pivot freely in the direction of feeding of the work, but are supposed to dig into the work when the direction is suddenly reversed. U.S. Pat. No. 1,074,198 shows a toothed roller journaled in inclined slots for upward movement to allow passage of the work under it. The teeth contact a rack in the housing that upon reversal of feeding direction, presumably forces the teeth down into the work. The patent is unclear how the feeding allows the toothed roller to remain in contact with the work. Another patent of interest is U.S. Pat. No. 1,089,901 which discloses an anti-kickback having a ratchet type one-way clutch. The working teeth are spring-biased into contact with the work.
U.S. Pat. No. 2,095,330 discloses an anti-kickback mounted on a splitter having a resilient rubber covering contacting the work.
Other patents of more general interest include: Nos. 2,479,998, 1,600,604 and 1,818,300 (all U.S.).
All the above are deficient in one or more ways as an anti-kickback; as mentioned above, the operation of the device of U.S. Pat. No. 1,074,198 is not clear--either the toothed roller rides up the rack and loses contact with the workpiece, or is allowed in some unexplained manner to become disengaged from the rack, in which case it would be ineffective. The U.S. Pat. No. 1,089,901 has a similar toothed roller that is free to turn in one direction and is prevented from turning in the other direction. This roller is spring-biased downwardly, and the spring force is constant for any one thickness of board. Presumably, this would leave a set of marks across the workpiece. At the same time, the effectiveness of the roller is directly dependent upon the spring.
The other patents mentioned above have similar drawbacks, necessitating the development of the instant invention.